Pneumatic fire detection system



Nov. 21, 1961 J. L. SWIFT 3,010,001

PNEUMATIC FIRE DETECTION SYSTEM Filed Nov. 21, 1958 5 Sheets-Sheet 1 FIG.2

IOA

I08 IOC n |2 HA I2A ma |2a nc I20 13 13' 13. %13A' 68%]38' |sc I3C' 11 If DETECTOR UNIT l6 Nov. 21, 1961 J. L. SWIFT PNEUMATIC FIRE DETECTION SYSTEM 3 Sheets-Sheet 2 Filed NOV. 21, 1958 FIG.3

Nov. 21, 1961 J. 1.. SWIFT 3,010,001

PNEUMATIC FIRE DETECTION SYSTEM Filed Nov; 21, 1958 5 Sheets-Sheet 3 FIG.5 K as United States Patent 3,010,001 PNEUMATIC FIRE DETECTION SYSTEM James L. Swift, Staten Island, N.Y., assiguor to American The present invention relates to fire alarm systems and more particularly to pneumatic fire alarm systems.

Pneumatic fire alarm systems have been well known and widely used for many years, one example of such a system being illustrated in Evans Patent 2,537,185 granted January 9, 1951. In such a system the increase in air pressure in a tubing with increases in temperature is used to actuate a detector, which in turn, transmits a fire alarm signalw In order to prevent transmission'of false alarms, such systems are usually compensated so that normal, relatively slow changes in pressure produced by normal increases in ambient temperature will not actuate the detector. In other words, the system responds only to a rate of rise in temperature in excess of some selected value.

While pneumatic fire alarm systems have been used wit-h great success for indoor protection, their use in protecting against outdoor fires and especially in the protection of outdoor power transformers and the like has not proven as satisfactory as desired. An important problem in this regard has been to develop suflicient pressure to give an alarm especially under adverse wind conditions. Difliculties have also been encounteredin con nection with the protection of very large volume indoor spaces such as aircraft hangars, armories and large auditoriums.

A principal object of the invention has been the provision of a novel and improved pneumatic fire alarmsystem which is especially adapted for outdoor fire protection and for the the protection of large indoor spaces.

Another object of the invention has been the provision of such a fire alarm system which is especially adapted lfOI protecting outdoor installations such as power transformers.

Another object of the invention has been the provision of such a fire alarm system which is especially adapted for the protection of outdoor installations such as chemical processing and storage areas, lumber yards, tank farms, parking lots, shipyards and shipboard areas.

Still another object of the invention has been the provision of a pneumatic fire alarm system for outdoor use which will produce an operating pressure rise even when wind velocity and direction minimize or prevent transmission of heat from a fire to the system by convection.

Another important object of the invention has been the provision of a device intended for inclusion in a pneumatic fire alarm system and which will be responsive to both convected and radiated heat from a tire to cause comprises a length of tubing filled with air, alarm actu ating means responsive to changes in air pressure within the tubing, and at least one heat responsive device. The heat responsive device comprises an elongated closed chamber filled with air and communicating freely with 7 surface of the chamber.

3,010,001 Patented Nov. 21, 1961 the tubing, the internal volume of the chamber being equal to the internal volume of a substantial length of the tubing. The heat responsive device also comprises a concave heat reflecting surface formed as a substantially spherical segment having an aperture less than the diameter of the sphere. The radius of the sphere is large in comparison to the diameter of the chamber. The chamber is mounted within the spherical segment and is disposed so that its axis substantially coincides with the principal axis of the reflecting surface and so that at least a major portion of the chamber is located inwardly of the principal focus of the heat reflecting surface.

The invention will now be described in greater detail with reference to the appended drawings, in which:

FIG. 1 is a schematic illustration of a heat responsive device in accordance with the invention;

FIG. 2 is a schematic illustration of a fire alarm system in accordance with the invention;

FIG. 3 is a front elevational view of a heat responsive device constructed in accordance with the invention;

FIG. 4 is a sectional view taken along the line 44 of FIG. 3; and

FIG. 5 is a perspective view of a fire alarm system in accordance with the invention arranged so as to protect an outdoor power transformer.

Referring now to the drawings and more particularly to FIG. 1, the heat responsive device is generally designated by the reference numeral 10 and comprises a concave spherical heat reflecting surface 11 and an elongated hollow cylindrical chamber 12 which is provided with tubes 13 and 13 for communicating with the other portions of a pneumatic fire alarm system.

The reflecting surface 11 is a spherical segment having a radius R and an aperture A which is less than the diameter of the sphere The surface 11 is preferably zfiormed from a metal which will not corrode substantially when exposed to the weather in outdoor locations and which is highly polished to facilitate reflection of heat rays incident thereon.

Heat rays from a fire, designated 14, strike the reflecting surface 11 and are reflected into contact with the chamber 12, causing the temperature of the latter to increase. A few rays, such as the one shown at 14' will contact the chamber 12 without reflection from the surface 11. A few other rays may contact the surface 11 at an incident angle such that they will not be reflected so as to impinge on the chamber 12. By making the chamber 12 relatively long, and by locating the chamber so that at least a substantial portion of its surface is located inwardly of the principal focus of the surface 11, few rays will mist the chamber 12. In the construction illustrated, the entire chamber 12 is disposed inwardly of the principal focus. The principal focus is determined from beams which approach the reflector parallel to the axis. Beams which approach the reflector at an angle to the axis focus at loci located inwardly of the principal focus. cipal focus gives a wide field angle, which is highly desirable. With an elongated chamber, advantage is taken of the relatively mushy or extended focus of a spherical reflector whose aperture is a substantial fraction of the diameter of the reflector, so that the heating eflFect of incident radiation is spread out. In order to be eflfective, the internal volume of the chamber 12 should correspond to the internal diameter of a relatively long length of pneumatic tubing. But to heat such a large chamber rapidly, incident radiation should be spread out over the By using 'a concave spherical reflector of large aperture and an elongated chamber (at least a major portion of which is disposed inwardly of the principal focus), a maximum amount of the radiation incident on the reflector will contact the chamber Locating the chamber 12 inwardly of the prinand the area of contact will be diffused over the surface of the chamber to yield a rapid rate of heating of the chamber. A spherical reflector is also desirable since it is not nearly so directionally sensitive as a parabolic reflector and it will generally be desirable to have as wide a field of fire sensitivity as possible.

By way of example only, the reflector 11 might have a radius of 7.55 inches and the reflector aperture A might be 13 inches. The chamber 12 might have a diameter of 1% inches and an axial length of 2% inches. The chamber 12 might have a wall thickness of 0.025 inch, yielding an internal volume equivalent to approximately 100 feet of conventional 0.05 inch ID. pneumatic tubing.

In addition to being subject to incident radiation from a fire, the chamber 12 is also subject to ambient temperature changes and hence will increase in temperature when heat is transferred thereto by convection from a fire. While under ideal conditions heat transfer by convection should be adequate to produce an alarm, adverse wind conditions could easily limit the heat transfer by convection so as to delay or prevent the giving of an alarm.

As the chamber 12 increases in temperature the pressure of the gas therein (normally air) will increase, thereby increasing the gas pressure in the pneumatic system with which the chamber communicates. This increase in pressure will actuate a detector as is customary in pneumatic fire alarm systems. Since such systems normally are compensated so as not to give alarm signals upon slow pressure increases such as occur with non-fire temperature changes, it is important that the chamber 12 be heated as rapidly as possible by radiant energy from a fire. If the temperature increase of the chamber 12 were too slow, the internal gas pressure change would be correspondingly slow and might fall within the compensating range of the pneumatic system and hence not give an alarm.

FIG. 2 illustrates in schematic form a detecting system incorporating fire detectors of the type shown in FIG. 1. Thus in FIG. 2 there are four detectors 10, A, 10B and 19C, each having a concave spherical reflector 11, a chamber 12 and tubes 13 and 13. The tube 13 is connected to the tube 13A through a tube 15; the tube 13A is connected to the tube 133 through a tube 15A; the tube 13B is connected to the tube 13C through a tube 153; and the tubes 13 and 13C are connected to a detector unit 16 through tubes 15C and 15D, respectively. The tubes 15 may be lengths of ordinary tubing not intended or disposed for fire detecting purposes, but preferably they will be pneumatic fire alarm tubing disposed so as to supplement the fire detecting action of the devices 10. While the chambers l2are shown connected in series, a parallel connection may be used if desired. A dead-end series connection may also be used, although the double-ended series connection illustrated is preferred since testing between the two ends of the loop will provide conclusive evidence of the integrity of the system.

The detector unit 16 includes means responsive to an increase of the air pressure within the pneumatic system for operating a fire alarm control unit, sounding device or transmitter. The detector unit 16 may beelectrically connected, as via conductors 17 and 18, to the means operated by it. The detector unit 16 may be of any of the well known types used in pneumatic fire alarm systems, for example, the one of the type shown in Evans Patent 2,275,949, granted March 10, 1942. Preferably, the detector unit will be connected in the usual way to a central station alarm system.

Referring now to FIGS. 3 and 4, there is shown in detail a preferred form of detecting device in accordance with the invention. shown atZtl and is provided with spaced holes to accommodate machine screws 21, 22 and 23, which serve to mount the reflector on a housing 24. The housing 24 comprises a cylindrical side wall 25, an integral end wall The spherical reflector surface is 26 having holes through which the screws 21-423 pass, and a removable cover 26 held in place by screws 27. The ends of the screws 21-23 carry nuts and washers as shown at 28 and 2-9. Spacing washers iii} are provided on the screws 21-23 between the housing end 26 and the reflector 20 to accommodate the curvature of the latter.

A mounting plate 31 is held in position outwardly of the reflector surface by bushings 32. and the screws 2l23. The plate 31 serves as the base of the pneumatic chamber 33, the balance of which is formed by a closed end cylinder 34. The plate 31 is provided with holes to accommodate pneumatic tubes 35 and 36, the open ends of which enter the cylinder 34. The tubes 35 and 36 correspond to the tubes 13 and 13 of FIG. 1 and serve to provide a pneumatic connection between the detector 33 and the balance of the system. The reflector 20 and the housing end wall 26 are provided with aligned holes to accommodate a bushing 37 through which pass the tubes 35 and 36. The connections between the tubes 35 and 36 and the detector chamber should be airtight so that changes in air pressure within the chamber are reflected in corresponding changes in the tubings. The reflector and chamber of FIGS. 3 and 4 may be constructed to the dimensions given in connection with FIG. 1, which dimensions have been found particularly desirable in connection with the detection of fires in outdoor power transformers.

FIG. 5 illustrates application of the system of the invention to the protection of an outdoor power transformer. In FIG. 5, the transformer is shown at 38 and is provided with a conventional sprinkler system designed 39. Four of the detecting devices of the invention are mounted at the respective corners of the sprinkler piping, the detectors 40, 41 and 42 being visible. The detectors are mounted so that they face the transformer and have their axes inclined at an angle of about 45. In this way radiation from fires on the transformer proper as well as from oil fires at the base of the transformer will impinge on the reflectors. With this mounting, direct radiation from the sun on the reflector surfaces will be minimized or eliminated.

An important advantage secured by the invention lies in the cumulativeeffect secured when using a plurality of the detectors of the invention. This cumulative effect arises because the detectors are interconnected by the pneumatic tubing. Thus in many cases there may be an appreciable time lag between the beginning of a fire and the time when it reaches a temperature suflicient to actuate a fixed temperature device or where the rate of temperature rise is sufficient to actuate an individual rate of rise device. However, with an installation in accordance with the invention it may well be that several detectors and the connecting pneumatic tubing are exposed to the fire. Each exposed detector will contribute some effect to the expansion of the air in the pneumatic tubing so that the cumulative or combined effect may originate an alarm sooner than would be the case with other systems where the full effect must be awaited at a single point.

In some cases it may be desirable to supervise the integrity of the system comprising the pneumatic tubing and detectors. Such supervision will preferably initiate a trouble signal should a pressure change other than a normal ambient pressure change or an alarm change occur. For example, the pneumatic system might be maintained at a slightly super-atmospheric pressure. Pressure decreases could then initiate a trouble signal while pressure increases would initiate alarm signals. Normal ambient changes in pressure should be suppressed to prevent spurious alarm or trouble signals. Supervision can of course be effected with the system maintained at a sub-atmospheric pressure, using a pressure increase less than that of an alarm to initiate a trouble signal.

' tubing and with the chambers of said other devices, the

internal volume of said chamber being equal to the internal volume of a substantial length of said tubing, and a concave heat-reflecting surface formed as a substantially spherical segment having an aperture less than the diameter of said sphere but constituting a substantial fraction of said diameter of said sphere, the radius of said I sphere being large in comparison to the diameter of said chamber, and said chamber being mounted within said spherical segment and disposed so that the axis thereof substantially coincides with the principal axis of said reflecting surface and so that at least a major portion of the surface of said chamber is located inwardly of the principal focus of said reflecting surface.

2. A fire alarm system, comprising a length of gasfilled tubing; alarm actuating means responsive to changes in gas pressure Within said tubing; and at least one heatresponsive device comprising an elongated cylindrical closed chamber made of heat-conductive material and being fill-ed with said gas and communicating freely with said tubing, the internal volume of said chamber being equal to the internal volume of a substantial length of said tubing, and a concave heat-reflecting surface formed as a substantially spherical segment having an aperture less than the diameter of said sphere but constituting a substantial fraction of said diameter of said sphere, the radius of said sphere being large in comparison to the diameter of said chamber, and said chamber being mounted within said spherical segment and disposedso that the axis thereof substantially coincides with the principal axis of said reflecting surface and so that the entire surface area of said chamber is located inwardly of the principal focus of said reflecting surface.

3. A fire-detecting device for use in a pneumatic firedetecting system, comprising an elongated closed chamber made of heat-conductive material and being filled with a gas, connecting means for affording gaseous communication between said chamber and a pneumatic fire-detecting system, the internal volume of said chamber being equal to the internal volume of a substantial length of the pneumatic tubing in said system, and a concave heat-reflecting surface formed as a substantially spherical segment having an aperture less than the diameter of said sphere but constituting a substantial fraction of said diameter of said sphere, the radius of said sphere being large in comparison to the diameter of said chamber,

is located inwardly of the principal focus of said reflecting surface.

4. A fire-detecting device for use in a pneumatic firedetecting system, comprising an elongated closed chamber made of heat-conductive material and being filled with a gas, connecting means for affording gaseous communication between said chamber and a pneumatic firedetecting system, the internal volume of said chamber being equal to the internal volume of a substantial length of the pneumatic tubing in said system, and a concave heat-reflecting surface formed as a substantiall-ytspherical segment having an aperture less than the diameter of said sphere but constituting a substantial fraction of said diameter of said sphere, the radius of said spherebeing large in comparison to the diameter of said chamber, and said chamber being mounted within said spherical segment and disposed so that the axis thereof substantially coincides with the principal axis of said reflecting surface and so that the entire surface area of said chamber is located inwardly of the principal focus of said reflecting surface.

5. A fire-detecting device for use in a pneumatic fire- -detecting system, comprising an elongated, cylindrical, closed chamber made of heat-conductive material and being filled with a gas, connecting means for affording gaseous communication between said chamber and a pneumatic fire-detecting system, the internal volume of said chamber being equal to the internal volume of at least about feet of the pneumatic tubing in said system, and a concave heat-reflecting surface formed as a substantially spherical segment having an aperture less than the diameter of said sphere but constituting a substantial fraction of said diameter of said sphere, the radius of said sphere being large in comparison to the diameter of said chamber, and said chamber being mounted within said spherical segment and disposed so that the axis thereof substantially coincides with the principal axis of said reflecting surface and so that the entire surface area of said chamber is located inwardly of the aperture of said reflecting surface. 7

References Cited in the file of this patent UNITED STATES PATENTS Kayser Mar. 21, 1916 

